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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Use of the TM tasseled cap transform for interpretation of spectral contrasts in an urban scene

Investigations are being conducted with the objective to develop automated numerical image analysis procedures. In this context, an examination is performed of physically-based multispectral data transforms as a means to incorporate a priori knowledge of land radiance properties in the analysis process. A physically-based transform of TM observations was developed. This transform extends the Landsat MSS Tasseled Cap transform reported by Kauth and Thomas (1976) to TM data observations. The present study has the aim to examine the utility of the TM Tasseled Cap transform as applied to TM data from an urban landscape. The analysis conducted is based on 512 x 512 subset of the Washington, DC November 2, 1982 TM scene, centered on Springfield, VA. It appears that the TM tasseled cap transformation provides a good means to explain land physical attributes of the Washington scene. This result provides a suggestion regarding a direction by which a priori knowledge of landscape spectral patterns may be incorporated into numerical image analysis.

Goward, S. N.↗
NASA NTRS1986

Space Shuttle Orbiter nose cap thermal analysis

The results of a Space Shuttle Orbiter nose cap entry aeroheating assessment, thermal analysis, and correlation of flight data using multidimensional thermal math models (TMM's) and a chemically reacting boundary-layer program are described in this paper. The object of this study was to verify and revise, if required, the nose cap design heating methods and the TMM's used for flight certification. Flight temperature measurements from two Orbiter vehicles, Columbia and Challenger, have been used in this analysis and provide the basis for verification and correlation of the aerothermodynamic environment. Nose cap thermal response predictions, using TMM's verified from certification tests, show that the aerothermodynamic environment can be satisfactorily predicted using accepted analytical methods.

Curry, D. M.↗
NASA NTRS1985

Gravistimulation-induced changes in current patterns around root caps

Changes in the electric current patterns around the root cap of corn following gravistimulation were determined using a vibrating probe. A transient increase in upward current in the cap was found following stimulation. The response began with a time lag similar to the presentation time, and was limited to the area of the root cap lateral to the statocytes. A physiological response as rapid as that reported by Behrens et al. (1985) was not observed.

Bjorkman, T.↗
NASA NTRS1985

Cytochemical localization of calcium in cap cells of primary roots of Zea mays L

The cellular distribution of Ca in caps of primary roots of Zea mays was examined during the onset and early stages of gravicurvature to determine its possible role in root gravitropism. Staining becomes associated with the portion of the cell wall adjacent to the distal end of the cell after five minutes, and persists throughout the onset of gravicurvature. The outermost peripheral cells of roots oriented horizontally and vertically secrete Ca through plasmodesmata-like channels in their cell walls. Data suggest that Ca is not transported laterally through the columella tissue,but rather that the movement of Ca to the lower side of caps of horizontally-oriented roots is at least partially through and/or on the mucilage of the cap, and via an electrochemical gradient. An important role in root gravitropism is indicated for Ca secretion by peripheral cells.

Moore, R.↗
NASA NTRS1985

The polar caps

According to the most common definition, the 'polar cap' is the region bounded by the average or statistical auroral oval. Studies of the effects of the interplanetary magnetic field (IMF) on various upper atmospheric phenomena are reviewed. The Antarctic region and the Arctic region represent an area for such investigations. Particular attention is given in this paper to those observations in the highest latitude region which provide some information concerning corresponding changes of the internal structure of the magnetosphere. A definition and working definition of the polar cap are considered along with the IMF and magnetospheric models, the entry of solar energetic electrons, statistical studies regarding the aurora, individual events, polar cap arcs, the cusp aurora, auroral electron precipitation, convection, ionospheric currents and field-aligned currents, the ionosphere, the thermosphere, polar rain, polar wind, and hopping motions of heavy ions.

Akasofu, S.-I.↗
NASA NTRS1986

Prediction filters for the Dst index and the polar cap potential

The technique of linear prediction filtering is used to create filters relating solar wind parameters to the Dst index and to the polar cap potential. The square root of solar wind dynamic pressure and the solar wind electric field together are found to account for nearly 70 percent of the Dst variance. The prediction filter for the polar cap potential requires the square of the solar wind velocity and the solar wind electric field as inputs. The results suggest that both polar cap potential and ring current injection are primarily controlled by the solar wind, and that substorm expansions do not play a major role in ring current injection.

Fay, R. A.↗
NASA NTRS1986

Solar wind control of the polar-cap voltage

The results of using various models to predict polar-cap potentials are reviewed. Quantitative predictions of merging rate, and hence of polar-cap voltage, based on subsolar merging models are reviewed, and tests of dayside merging models and their results are reexamined. Predictions and tests of cusp merging models are discussed. Two new empirical formulas for the dependence of the asymptotic polar-cap potential on the IMF are presented, and predictions of the dependence of dayside and lobe merging voltages on the IMF are derived from the antiparallel merging hypothesis.

Reiff, Patricia H.↗
NASA NTRS1988

Wing flutter calculations with the CAP-TSD unsteady transonic small disturbance program

The application and assessment is described of CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code for flutter prediction. The CAP-TSD program was developed for aeroelastic analysis of complete aircraft configurations and was previously applied to the calculation of steady and unsteady pressures. Flutter calculations are presented for two thin, swept-and-tapered wing planforms with well defined modal properties. The calculations are for Mach numbers from low subsonic to low supersonic values, including the transonic range, and are compared with subsonic linear theory and experimental flutter data. The CAP-TSD flutter results are generally in good agreement with the experimental values and are in good agreement with subsonic linear theory when wing thickness is neglected.

Bennett, Robert M.↗
NASA NTRS1987

How dirty is Mars' North Polar cap, and why isn't it black

Global studies of Mars seem to indicate conclusively that the seasonal polar caps are CO2, and that the residual polar cap is H2O. Viking Lander measurements are discussed, focusing on dust and water effects. The composition and annual budget of the residual caps and the local volatile transport should be well addressed by the complement of nadir-looking instruments on the Mars Observer.

Kieffer, Hugh H.↗
NASA NTRS1987

Martian north polar cap and circumpolar clouds - 1975-1980 telescopic observations

Observational data on the late-winter/spring sublimation and recession of the north polar cap of Mars are analyzed statistically. Ground-based photographic data obtained by the International Planetary Patrol during the oppositions of 1975, 1978, and 1980 are compiled in tables and graphs, and Viking data from the 1977-1978 and 1980 recessions are included for comparison. The results indicate that the recession of the cap from its maximum extent (near 55 deg N) reaches a plateau during midspring. The end of this plateau is associated with (1) a sharp increase in circumpolar cloud cover (suggesting that the cap is the water source) and (2) a probable reversal of the northern-hemisphere meridional wind (as observed by Kahn, 1983).

James, Philip B.↗
NASA NTRS1988

Wing flutter calculations with the CAP-TSD unsteady transonic small disturbance program

The paper describes the application and assessment of the recently developed CAP-TSD transonic small-disturbance code for flutter predicition. The CAP-TSD program has been developed for aeroelastic analysis of complete aircraft configurations and was previously applied to the calculation of steady and unsteady pressures with favorable results. Flutter calculations are presented for two thin swept-and-tapered wing platforms with well-defined modal properties. The calculations are for Mach numbers from low subsonic to low supersonic values, including the transonic range, and are compared with subsonic linear theory and experimental flutter data. The CAP-TSD flutter results are generally in good agreement with the experimental values and are in good agreement with subsonic linear theory when wing thickness is neglected.

Bennett, Robert M.↗
NASA NTRS1988

A model for multiple throat structures in the polar cap flow entry region

A two-dimensional ionospheric convection model has been developed to produce convection patterns for southward interplanetary magnetic field (IMF) and a positive or negative IMF y component. The model consists of a movable, shear convection reversal boundary with a gap in it where flux enters the polar cap. The sign of IMF B(y) determines the dayside gap geometry. This simple model is used to simulate measured ionospheric flows from the DE 2 satellite. Roughly 35 percent of DE 2 passes that cross the dayside between 0800 and 1400 hours MLT cannot be modeled with a single narrow flow entry region. By comparing model calculations and the measured ion flows, it is shown that the dayside flow entry region to the polar cap typically spans several hours in local time. The electric field can concentrate along portions of the polar cap entrance and weaken between the concentrated regions, thus forming multiple 'throats'.

Moses, J. J.↗
NASA NTRS1990

Mariner 9 observations of the south polar cap of Mars - Evidence for residual CO2 frost

The first spacecraft observations of the south residual polar cap of Mars were obtained by the Mariner 9 orbiter during the Martian southern summer season, 1971-1972. Analyses of Viking orbiter observations obtained 3 Mars years later have shown that residual carbon dioxide frost was present at the south polar cap in 1977. In this study, Mariner 9 infrared interferometer spectrometer spectra and television camera images are used in conjuction with multispectral thermal emission models to constrain the temperatures of dark bare ground and bright frost regions within the south residual cap. The results provide strong evidence that carbon dioxide frost was present throughout the summer season despite the fact that the residual frost deposits observed by Mariner 9 were less extensive than those observed by Viking.

Paige, D. A.↗
NASA NTRS1990

Zonally averaged thermal balance and stability models for nitrogen polar caps on Triton

Voyager four-color imaging data of Triton are analyzed to calculate the bolometric hemispheric albedo as a function of latitude and longitude. Zonal averages of these data have been incorporated into a thermal balance model involving insolation, reradiation, and latent heat of sublimation of N2 ice for the surface. The current average bolometric albedo of Triton's polar caps is 0.8, implying an effective temperature of 34.2 K and a surface pressure of N2 of 1.6 microbar for unit emissivity. This pressure is an order of magnitude lower than the surface pressure of 18 microbar inferred from Voyager data (Broadfoot et al., 1989; Conrath et al., 1989), a discrepancy that can be reconciled if the emissivity of the N2 on Triton's surface is 0.66. The model predicts that Triton's surface north of 15 deg N latitude is experiencing deposition of N2 frosts, as are the bright portions of the south polar cap near the equator. This result explains why the south cap covers nearly the entire southern hemisphere of Triton.

Stansberry, John A.↗
NASA NTRS1991

The hemispherical asymmetry of the residual polar caps on Mars

A model of the polar caps of Mars was created which allows: (1) for light penetration into the cap; (2) ice albedo to vary with age, latitude, hemisphere, dust content, and solar zenith angle; and (3) for diurnal variability. The model includes the radiative effects of clouds and dust, and heat transport as represented by a thermal wind. The model reproduces polar cap regression data very well, including the survival of CO2 frost at the south pole and reproduces the general trend in the Viking Lander pressure data.

Lindner, Bernhard Lee↗
NASA NTRS1993

Caps Seal Boltholes On Vacuum-System Flanges

Sealing caps devised for boltholes on vacuum-system flanges. Used in place of leak-prone gaskets, and provide solid metal-to-metal interfaces. Each sealing cap contains square-cut circular groove in which O-ring placed. Mounted on studs protruding into access ports, providing positive seal around each bolthole. Each cap mates directly with surface of flange, in solid metal-to-metal fit, with O-ring completely captured in groove. Assembly immune to misalignment, leakage caused by vibration, and creeping distortion caused by weight of port. O-ring material chosen for resistance to high temperature; with appropriate choice of material, temperature raised to as much as 315 degrees C.

Roman, Robert F.↗
NASA NTRS1992

Glacio-isostatic crustal movements caused by historical volume change of the Vatnajokull ice cap, Iceland

Measurements of the lake level of Lake Langisjor at the SW edge of the Vatnajokull ice cap indicate a tilt of 0.26 +/- 0.06 microrad/yr away from the ice cap in the years of 1959-1991. The tilt is too large to be explained as an elastic Earth response to ice retreat this century, or to be caused by change in the gravitational pull of the ice cap, but it can be explained by sub-lithospheric viscous adjustment. Regional subsidence in historical times in SE Iceland can similarly be attributed to viscous adjustment resulting from the increased load of Vatnajokull during the Little Ice Age. The inferred sublithospheric viscosity is 1 x 10 exp 18 - 5 x 10 exp 19 Pa s.

Sigmundsson, Freysteinn↗
NASA NTRS1993

Spatial variation in the seasonal south polar cap of Mars as observed by Mariner 7

Spatial variations in infrared spectra of the seasonal south polar cap of Mars were noted by the original Mariner 7 IRS instrument team as well as in subsequent examinations of the Mariner 7 data set. Up to now, however, there has been little effort to synthesize this information to understand variations in the south seasonal cap as a function of position or latitude. An attempt to quantify the spectra is made by providing estimates of CO2 grain sizes as well as upper limits on the amount of water frost contained in the polar collar. The variation in brightness at two wavelengths as well as the band depth of a weak CO2-ice feature at 2.28 microns as a function of spectrum number or subsequent location on the cap is presented. The full spectra, corrected only for the solar incidence angle, of three of the most significant areas are compared.

Calvin, Wendy M.↗